So, every other day, Mark and Frank were sent down to St.Mark's in the canoe for the mail, allowed to take their guns and fishing-tackle with them, and given permission to stay out as long as they chose, provided they came home before dark.

Sometimes Ruth was allowed to go with them, greatly to her delight, for she was very fond of fishing, and always succeeded in catching her full share.

While the boys were thus absent, Mr.Elmer took charge of whatever work Mark might have been doing, and Jan always managed to be within sound of the ferry-horn.
On one of their first trips down the river Mark had called Frank's attention to the head of a small animal that was rapidly swimming in the water close under an overhanging bank, and asked him what it was.
For answer Frank said, "Sh!" carefully laid down his paddle, and taking up the rifle, fired a hasty and unsuccessful shot at the creature, which dived at the flash, and was seen no more.
"What was it ?" asked Mark.
"An otter," answered Frank, "and his skin would be worth five dollars in Tallahassee." "My!" exclaimed Mark, "is that so?
Why can't we catch some, and sell the skins ?" "We could if we only had some traps." "What kind of traps ?" "Double-spring steel are the best." "I'm going to buy some, first chance I get," said Mark; "and if you'll show me how to set 'em, and how to skin the otters and dress the skins, and help do the work, we'll go halves on all we make." Frank had agreed to this; and when Mark went to Tallahassee he bought six of the best steel traps he could find.

These had been carefully set in likely places along the river, baited with fresh fish, and visited regularly by one or the other of the boys twice a day.

At first they had been very successful, as was shown by the ten fine otter-skins carefully stretched over small boards cut for the purpose, and drying in the workshop; but then, their good fortune seemed to desert them.
As the season advanced, and the weather grew warmer, they began frequently to find their traps sprung, but empty, or containing only the foot of an otter.